Air-conditioning control system



Feb. 10, 1953 J. w. SMITH 2,628,076

AIR-CONDITIONING CONTROL SYSTEM Filed Jan. 22, 1949 2 SHEETS-SHEET 1 JNVENTOR. JAMES W. SMITH 1953 J. w. SMITH AIR-CONDITIONING CONTROL SYSTEM Filed Jan. 22, 1949 2 SI-IEETS--SHEET 2 IN V EN TOR.

JAMES W. SMITH ATTORNEY Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE AIR-CONDITIONING CONTROL SYSTEM James W. Smith, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application January 22, .1949, SerialaNioJ 72,243

pensated for either sequence.

form of the present invention.

Figure 2 .is a schematic representation of a modified form of the present invention.

The air conditioning system shown in Figure l of .the drawing is rather conventional and In air conditioning, it is frequently -.desirable 5 comprises .a'return air inlet Ill, a fresh air inlet to control a heating system and a coo-ling sys- H, a blower vl2 and a discharge conduit [3. A tern in sequence to hold the-space temperature cooling coil or evaporator l5 and a steam -coil within desired limits and, to keep "these .limits or heater 16 are located in conduit [3 and are within the desired limits, compensation is rearranged to temper the air passing throughsaid quired. Also,-in many instances, it is desirable to conduit. vary the control point of a space thermostat in Evaporator I 5 is supplied with refrigerant by a predetermined manner, compensation also bea compressor 11 driven by an electric motor i8, ing necessary for this. However, proper comthe refrigerant being pumped by the compressor pensation for a-cooling system is generally in an through a condenser IS, a thermostatic expanopposite direction from that needed for a heat- 15 sion valve'20,coil l5 and back to the compressor. ing system and is often different in amount. :It Motor I8 is energized by the circuit: line Wire is thus a principal object of this invention to 22, switch 23 of relay'24, wire 25ymotor l8, wire provide a control system for both a heating sys- 25 and line wire 21. The energization of winding tem and a cooling system wherein proper com- .28 of relay 24 will be described later :asa'funcpensation is provided at all times. tion of the present control system.

It is an additional object to provide a control Heating coil It is supplied with steam through system for'both heating and cooling wherein the apipe 3i, under control .of .a motorized valve 32, control pointor'throttling ranges may'overlap or from a suitable source, not shown. Valve 32 is may bespaced apart a desired amountbut wheredriven by a conventional, geared, two-phase rein the compensation remains correct. 25 versible motor 33, motor 33 also driving a cam An additional object, similar to that above, .34 and a pairof follow-up:potentiometers 35 and is the provision of a control system for .both 36. Cam 34 serves to position a pivoted lever 33 heating and cooling wherein the throttling having mounted thereon a Pa Of rc y ranges or control points may overlap but-wherein switches 49 and 4!, the cam being so arranged .both heating and cooling are provided at the that both switches All and 4! close their contacts same time when necessary for humidity control. when valve 32 is fully closed, the valve "being It is a further object to provide control appaslightly open .as shown, and the contacts are ratus for an air conditioning system compensated open at all other positions of said valve. :Motor for variations in outside temperature and also 33 simultaneously positions wiper -31 to the .excompensated for additional :cooling of the cir 35 treme right of resistor 39 of follow-up potenculating air .during operating conditions involvtiometer 35 and wip r 2 t0 the me right ing humidity control. of resistor 43 of .follow-up potentiometer 3%,

.It is also an object to provide va-rcontrol appaslightly beyond the position shown, when the ratus comprising a network circuit having aJplu- Valve iS-010S8d,the p and 42 being driven rality of outputs .for controlling a plurality of to the left extreme of resistors -39 and 43, p devices andihavinga convenient and efiectivecatively, as t e va e is p ed .pacity balance arrangement for adjusting the Motor '33 is controlled bya discriminat yp network to a'null point. amplifier 45 including-a pair-of relays it and 41,

It is'an additional object to provide a switchone of the relays being operated-when an input ing arrangement in a control system which posi- 45 signal of one phase is impressed on input termitively provides the correct compensation for the nal 48 and the other relay being operated with system at all times. an input signal of opposite phase is impressed It is another object to provide an improved on said input terminal, the other input terminal automatic air conditioning control system oper- 49 of the amplifier being connected through wire able on a heating sequence, cooling sequence or a 50 '50 to'ground 5i. While any conventional dishumidity control sequence. criminator type'relay or amplifier device may be These and other objects will appear upon a used, an electronic amplifier such as described in study of the followingspeciflcation and drawings Upton Patent No. 2,423,534, issued July '8, 1947, wherein: has been found quite satisfactory.

Figure 1 is a schematic representation of one Relay 2'4 -is normally controlled by an amplifier =53 including a relay 54 and'hav'ingan'input terminal 55 and a grounded input terminal 56, this amplifier being similar to 45. Relay 24 may also be operated by relay 6| controlled by humidistat 62, relay having a Winding 63 and a switch 64. Humidistat '62 includes a mercury switch 65 operated by a moisture sensitive hair element 68,

switch 65 being closed when the relative humidity exceeds a predetermined value for which device 82 is set.

Humidistat 62 also cooperates with mercury switch 4| to control relay 68, this relay including a winding 69 and a pair of switch blades 71 and 12. Switch blade 12 coacts with in contact 13 and switch blade H coacts with in contact l4 and out contact 75, blade 12 and contact 73 controlling a holding circuit for the relay 68 and blade ii and its contacts determinin whether amplifier $5 is being controlled in a normal heating sequence or a reheat sequence.

Amplifiers and 53 are controlled by an electrical network circuit generally identified by the numeral 88, circuit 89 having input terminals 8| and 82 energized from secondary winding 83 of transformer 8d, primary winding 85 of this transformer being connected to line wires 22 and 21 by wires 86 and 31, respectively. Network 80 includes a plurality of parallel branches, the first branch comprising a temperature responsive resistor 9| used as a room thermostat, a calibrating potentiometer having a resistor 92 and a wiper 93 connected to ground 5!, and a fixed resistor 94, this branch being connected across terminals or sides BI and 82 of the network. A cooling branch of the network comprises an outside compensator which is a temperature responsive resistor 96, a fixed resistor 91, a fixed resistor 98, a fixed resistor 99, a variable resistor fill and a fixed resistor IE2, this branch also being connected across input terminals or sides 8! and 82 and in parallel with the aforementioned branch. Re-

sistor 43 of follow-up potentiometer 36 is connected in parallel with resistor 98, and resistor 163 of manually adjusted potentiometer IE4 is also connected in parallel with resistor 98. Wiper H35 of potentiometer I94 is connected through wire I86, resistor I91 of a high resistance potentiometer Hi3, fixed resistor m9, and wire to ground 5|. Wiper MB of potentiometer IE8 is connected by wire Hi' to input terminal of amplifier 53.

The heat control branch of network 83 com- 4,!

prises, reading from input terminal or side 8|, fixed resistor H4, variable resistor H5, fixed resistor H6, fixed resistor Ill connected in parallel with resistor 39 of follow-up potentiometer 35,

fixed resistor H8, outside compensator, or temperature responsive resistor H9, discharge compensator 28, likewise formed of material having a relatively high temperature coefficient of resistance, and the opposite input terminal or side 82 of the network. Wiper 31 of follow-up potentiometer 35 is connected by wire 22 to out contact '55 of relay 68 and wiper 42 of follow-up potentiometer 36 is connected by wire I23 to in contact i l of said relay. Wiper 93, connected to ground 5! comprises one output terminal of network so and wiper 3? of follow-up potentiometer 35 comprises the other output terminal of the network when on a normal heating cycle. Wiper 42 of follow-up potentiometer 36 comprises the ungrounded output terminal of the network circuit when on a reheating cycle, and wiper H35 of manually adjusted potentiometer IE4 comprises the output terminal for the cooling bran-ch of the network circuit, with potentiometer #08 being interposed between wiper I55 and amplifier 53 as a sensitivity control for adjusting the intensity of the signal that can be imposed on amplifier 53 by a predetermined unbalance in network 80.

In addition to the above parallel branches of network Bil, resistor I26 of potentiometer 521 is connected across the input terminals 8| and 82, resistor I26 being of relatively high value. Wiper I28 of this potentiometer is connected through capacitor I29 to ground 55, the adjustment of wiper l28 across resistor I25 serving to alter the capacity balance of the bridge network and is used to establish an optimum condition of balance in the network upon installation, this optimum condition of balance being determined by adjusting the various calibrating potentiometers in the network proper to obtain minimum signals and then further adjusting wiper 28 to reduce these minimum signals to the lowest possible value. This adjustment is usually made upon installation and seldom needs repeating thereafter and is an efiective and simple way to balance the capacity effects of the bridge due to long leads and the like for remote devices such as the previously mentioned compensators.

As an example of resistance and capacity values found useful in the present network circuit the following table of values is submitted. Obviously these values are for illustration only.

Table Ohms ! 1 Capacitor Primary winding (36 of transformer iE i and amplifier 45 and 53 are connected to line wires 22 and 21, as shown. To better show the function of the present control system, its operation will now be discussed.

Operation With the apparatus arranged as shown and in operation, a blower i2 is inducing a fiow of return air through inlet it and a fiow of fresh air through outside air inlet H and is discharging the air through coils i5 and it into the distribution portion of the air conditioning system, not shown. As switch 23 of relay 2B is open. the refrigerating apparatus is not being operated hence there is no cooling due to coil l5. However, steam valve 32 is slightly open, hence there is a small amount of heat being furnished by coil 15. Assuming that network 8!! is so adjusted that the desired room temperature is when the outside temperature is 70 and that the room temperature may be permitted to increase to when the outside temperature rises to and that the room temperature may rise to 74 when the outside temperature is 0", it may now be fur ther assumed that the apparatus is now operating at an outside temperature of about 55. If the outside temperature should now drop below 65", it seems obvious that compensators H9 and 29 will both reflect the lower temperature by lowering their resistance, thus unbalancing network 80 and causing a signal to be impressed on input terminal 48 of amplifier 45 through wiper 31, wire I22, contact 15, wiper 1I, wire I3I and input terminal 48. As previously mentioned, a signal impressed on input terminal 48 of amplifier 45 causes one or the other of relays 46 and 41 to be operated, the phase of the input signal determining which of the relays will be pulled in. Rather than discuss the present network in terms of phase relation, however, it is more convenient to discuss this network in terms of potentials at a half cycle instant, it being obvious that the potentials will be reversed at the next half cycle instant and that like potentials will indicate, :in the actual circuit, like phase relations, whereas opposite potentials at the instant in question will indicate reverse phases. With this assumption, let it now be assumed that at the half cycle instant in question, input terminal or side M of network 80 is positive and input terminal or .side 82 of the network is negative and further assume that a positive signal at amplifier input terminal 48 causes operation of relay 43 to drive motor 33 in a valve closing direction and a negative signal at terminal 48 causes operation of relay 41 to energize motor 33 in a valve opening direction. With a decrease in outside temperature and a consequent lowering of the resistance of compensators H9 and I20, it seems obvious that wiper 3'! will become more negative relative to ground 5i than previously, hence a negative signal is impressed on terminal 43 by the aforementioned circuit. This causes relay 41 to close its contacts and thus energize motor 33 by the vcircuit: transformer secondary winding I 33 of transformer I34, wire I35, wire I36, relay 41, wire I31, motor 33 and ground wire 50. As before mentioned, energization of motor 33 in this manner causes it to operate in a direction to open valve 32. As valve 32 is opened, additional steam is supplied coil I3 to furnish heat to offset the decrease in outside temperature. In addition, cam 34 is operated in a direction to further raise pivoted lever 38, hence switches 40 and M remain open. In addition, wipers 31 and '42 are .adjusted to the left across their respective resistors, wiper 3'5 tending to become less negative as it is advanced to the left across resistor 39. When the additional negative signal caused by the cooling of resistors II9 and I20 is 'rebalanced by the leftward movement of wiper 31, the negative signal impressed on amplifier terminal 48 is eliminated and equilibrium is again achieved with valve 32 being slightly more open than before. If the additional opening of valve 32 was not enough to counteract the effect :of the fall in outside temperature and the room temperature also diminishes, thereby diminishing the resistance of resistor BI, it appears that this decrease in resistance causes terminal or side 8-1 to be less positive relative to ground than it previously was, hence the decreased positive potential of the left side of the network results in wiper 31 again becoming negative relative to ground 54 hence relay 41 is again energized and drives motor 33 in a further valve opening direction until additional leftward movement of wiper 31 again rebalances the network and wipes out the negative signal, thus deenergizi-ng relay 41 and stopping further movement of the motor.

With the system now in equilibrium and with additional heat being supplied, it may now be considered that the relative humidity in the space being treated increases beyond the desired an elongation of the hair element 66 thus permitting a clockwise movement of pivoted switch 65 and a closing of its contacts. This causes energization of relay 6I by the circuit: secondary winding I33, wire I39, switch 65, wire I40, wire I4I, winding 33 of relay BI, and wire I42 to ground wire 50. Relay 6% then causes energize.- tion of relay 24 by the circuit: secondary winding I33, wire I35, wire I44, wire I45, switch 64 .of relay 3I, wire I40, wire I41, winding 23 of relay 24 and wire E48 to ground wire 50.. .As previously mentioned, the energizing of relay 24 causes .operation of the refrigerating system by a circuit previously traced. Operation of the refrigerating system causes cooling at .coil l5 thus tending to condense out moisture in the air being delivered through the coil. In addition, the cooling due to coil I5 causes a reduction in temperature of the air effecting compensator I23 hence .the lowered resistance of this compensator causes wiper 31 to again become negative relative to ground thereby impressing a negative signal on terminal 43 of amplifier 45 and causing energization of .relay 41 and a further opening of steam valve 32 to counteract the effect of the cooling due to coil I5. Upon the relative humidity in the space being treated decreasing below the value for which humidistat 62 is set, and thereby causing a contraction .of hair element 66 and an opening of the contacts of switch 65, relay BI is \deenergized as is relay 24, thereby stopping the refrigerating system. Normal heating then continues, with valve 32 being slightly closed as compensator I20 comes-up to outside air temnerature.

If the "outside temperature should now rise, .resistors I I9 and I20 increase in temperature and resistance and thereby tend to make wiper .3? positive relative to ground and cause a positive signal to be impressed on terminal 48 by the aforementioned circuit. This causes an energization of relay 46 and the energization of motor 33 by the circuit: secondary winding I33, wire I35, wire I36, relay 46, wire -I5I, motor 33 and ground wire 50. This causes motor 3.3 to drive valve 32 in a closing direction and also causes .a rebalancing of the network by driving wiper 31 to the right across resistor 39. Obviously, the increase in outside temperature will also tend to cause an increase on the inside temperature and the increase in temperature of resistor -9I causes it to increase in resistance and thereby tends to increase the positive potential of the left side of the network, thereby tending .to make wiper 31 positive with respect to ground 5,! and again causing a positive signal to be impressed on :ter-

.minal 48, with .a consequent further closing of comfort. Obviously, as the room temperature increases, the steam valve is driven in a closing direction and, as the outside temperature increases, the valve is driven in a further closing direction because of the lowering of the control point for the space. However, should compensation in this direction be continued through a cooling cycle so that the control point for the space temperature would continue to diminish as the outside temperature increased, it seems obvious that a relatively low space temperature would be required when the outside temperature is quite high. This is obviously contrary to the requirements for a good air conditioning system hence the compensation for the cooling system must be diiierent from that described above.

With the increase in outside temperature and the consequent increase in space temperature, we may now consider that valve 3'2 has been driven to a completely closed position by motor 33, wipers 3! and 42 are at the extreme right of their respective resistors and cam 34 has new advanced sufi'iciently to lower pivoted arm 38 sufficiently to close the contacts of switches 40 and H.

While on the heating cycle, amplifier 53 has also been energized and, because the compensated cooling control point for the network is below the space temperature, due to the relatively low outside temperature, relay 54 is pulled in, but because the contacts of switch 40 are open, relay 24 can not be energized by the amplifier 53, hence there has been no cooling.

With the space temperature at about 70, the established control point for the space, and with the outside temperature somewhat above 70, it appears obvious that the left side of network 80 is at a relatively high positive potential relative to ground 5I.

Because of the relatively high temperature of compensators H9 and I20, wiper 3? is positive relative to ground, hence relay 4B of amplifier 45 remains energized to keep valve 32 closed. Also, due to the relatively high resistance of compensator 96, the increase in resistance of BI is ofiset by the increase in resistance of 96 hence wiper I05 is at substantially ground potential and there is no output signal from the network for operating amplifier 53. Amplifier 53 is operative in the same manner as amplifier 45 with relay 54 being relative to ground and the resulting signal impressed on terminal 55 through wire I06, resistor I01, wiper H and wire III to terminal 55 'causes energization of relay 24 by the circuit:

secondary winding I33, wire I35, wire I44, wire I53, relay 54, wire I54, switch 40, wire I55, wire I4I, winding 28, and wire I48 to ground wire 50. Energization of relay 24 starts motor I8 and compressor I! by a circuit previously traced and thereby causes cooling of the air discharged through conduit I3. If the outside temperature should now rise considerably without a corresponding increase in room temperature, it appears that wiper I will then tend to become negative relative to ground and a negative signal thus impressed on terminal 55. No signal or a negative signal impressed on terminal 55 will, of course, cause a deenergization of relay 54 and a stopping of the refrigerating system, thus permitting an increase in the space temperature as the outside temperature rises due to the compensating effect of resistor 95. However, if the outside air temperature should fall rather than rise, or if the space temperature should be relatively high, wiper I05 then again becomes positive relarespectively and this establishes a holding circuit for the relay by shunting switch 41 through wire I52, blade I2 and contact '13, hence relay 68 will then remain energized so long as switch 55 is closed, even if switch M is opened due to opening of valve 32.

The engagement of wiper II with in contact I4 connects rebalance potentiometer 38 to amplifier by the circuit: wiper 42, wire I23, contact I4, blade II, wire I3! and input terminal '18 of amplifier 45. Due to the extreme right position of wiper 42 on resistor 53, said wiper tends to be negative relative to ground 5| and, as a negative signal on input terminal 48 of amplifier 4'5 has been described as causing energization of relay 4?, the consequent opening of steam valve 32 causes heat to be supplied to the air after its cooling by coil I5. Then, as valve 32 is opened, wiper 42 is advanced to the left across resistor 43 to rebalance the network. However, the rebalancing caused by wiper 42 has no eiiect on the potential of wiper I05 hence, so long as the space temperature remains sufliciently high to keep the wiper I05 positive, relay 54 remains in but ineffective. Thus, regardless of the outside temperature, when the relative humidity of the space is high and the contacts of switch 55 are closed, heating and cooling may be provided at the same time. However, this reheat cycle, for that is what it amounts to, is different from that previously described for the compensation for the network is now due to resistor 55 rather than resistors H9 and I25, as previously described. The efiect of this is to control the heating of the space on the basis of cooling compensation, thereby requiring variations in space temperature based on outside temperature with the change being in the opposite direction to that previously described, the change to cooiing compensation being the function of relay 58. Further, because switch 4i is in the energizing circuit for relay 68, this relay can be pulled in by humidistat 52 only when valve 32 is closed. The continued operation of the refrigerating system obviously tends to reduce the temperature of coil I 5 and thereby condense out excess moisture, and the reheating of the air by coil It causes a decrease in relative humidity. Upon humidistat 62 being satisfied and the contacts of switch 65 opened, relay 58 is deenergized thus breaking the holding circuit through switch blade i2 and contact 13. Further, blade H again engages contact '55 and puts rebalance potentiometer 35 in the circuit with amplifier 55. Because the space temperature and outside temperature are above the temperatures required to give a negative signal on this part 0.1? the circuit, the resulting positive signal on wiper 3'1 and input terminal 43 of the amplifier causes energization of relay 38 and the closing of valve 32 by motor 33. The normal cooling cycle resumes and the refrigerating apparatus is continued in operation until wiper I55 is no longer positive relative to ground at which time the operation of the refrigerating apparatus ceases, as. above described.

Figure 2 The air conditioning system shown in Figure 2, including the refrigerating apparatus and steam heating apparatus is similar to that of Figure 1. In addition, the amplifier for controlling the motor valve and the amplifie for controlling the refrigerating apparatus are also similar, as is the humidistat, and like parts have similar numbers. However, in this figure, the network circuit I65 used for controlling the apparatus is diiferent to some extent although the energizing transformer and the lower portion of the network is essentially the same as that of Figure l and has been similarly numbered. In this network circuit, a variable resistor I66 is provided between resistor 9| and input terminal ill, and a circuit comprising wires I61, switch I68, and wire I69 is arranged in shunt relation to said resistor so that, when switch I68 is closed, resistance I66 is not efiective.

The upper portion of the network comprises a first branch having a variable resistor F, a fixed resistor I12, a variable resistor I13 in shunt relation to resistor 39 of follow-up potentiometer '35, resistor I14 of potentiometer I15, compensating resistor I16 having a relatively high temperature coefiicien-t of resistance, and fixed resistor 111, this branch being connected across input terminal or sides 8| and 82. Wiper I18 of potentiometer I is connected by wire I19 to out contact I86 of relay NH and is arranged to be engaged by switch blade I62 of said relay. Also, wiper 31 of follow-up potentiometer is connected by wire I83 to out contact I84 of relay IBI and is engageable by switch blade I85. The upper branch of the network I65 comprises a fixed resistor I31, compensating resistor I88 having a relatively high temperature coemcient of resistance, variable resistor I89 connected in shunt relation to resistor 43 of follow-up potentiometer 36, resistor I9I of potentiometer I92, fixed resistor I93, and variable resistor I94, this branch also being con-- nected in parallel to the previous branches and acros input terminals or sides BI and 82 of network I65. Wiper I95 of potentiometer I92 is connected by wire I96 to in contact I91 of relay I8I and wiper 42 of follow-up potentiometer 36 is connected by wire I98 to in contact I99 of said relay. Switch blade I82 of relay I8I is connected through resistor 21 of potentiometer 262 and fixed resistor 266 to ground wire 59, wiper 263 of said potentiometer being connected by wire 234 to input terminal 55 of amplifier 53, input terminal 56 of said amplifier being connected to ground through wire 56. Switch blade I85 of relay I8I is connected by wire 266 to input terminal 48 or amplifier 45,

input terminal 49 of said amplifier being connected to ground through wire 56. Relay I8I is controlled by switch 2I4 of thermostat 2I5 located in duct II and therefore responsive to outdoor air temperature. Thermostat 2I5 is adjusted to close switch 214 at temperatures of 70 and above, for example, and to open said switch at temperatures below 70. Amplifiers and 53 are energized from line wires 22 and 21, as in the previous example and the primary windings of transformers 84 and I34 are similarly energized from said line wire.

Assuming the present apparatus is in operation and in equilibrium with the room temperature at near '70 degrees and an outside temperature suffioiently low torequire a small amount of steam through valve 32, and further assuming that the network circuit is adjusted to provide substantially the same compensation as provided previously and that the capacity balance potentiometer I21 has been adjusted for the most optimum null signal when the bridge is balanced, it now appears that the refrigerating apparatus is not operating because switches 23 and 213 are both open and, because the switch 2M of outside air thermostat 2 I 5 is open, the system is on a heating cycle and wiper 31 of follow-up potentiometer 35 is connected to input terminal 46 of amplifier 45 through wire I83, out contact I64, switch blade I and wire 266 to said input terminal. If the outside temperature should now diminish, thereby lowering the resistance of resistor I16, it appears that a signal will be impressed on input terminal 48. With'the same phase relation existing in network I65 as discussed previously, and the left side of the network at a positive potential and the right side at a negative potential at the half cycle instant in question, it appears that a decrease in resistance of resistor I16 tends to make wiper 31 negative relative to ground 5|, hence a negative signal is impressed on input terminal 46, thereby causing relay 41 to pull in and energize motor 33 by the circuit: secondary winding I33, wire-2H, wire 2I8, wire 2I9, relay 41, wire I31, motor 33 and wire 50 to ground. This causes operation of motor 33 in a direction to open valve 32 and to drive wipers 31 and 42 of follow-up potentiometer 35 and 36, respectively, to the left across aid resistors. As wiper 31 is driven from the left across resistor 43,11: becomes less negative relative to ground and the signal is eventually rebalanced, as in the previous example. Likewise, a decrease in room temperature causes wiper 31 to become negativ relative to ground and causes a negative potential to be impressed on input terminal 46 thereby causing energization of motor 33 in a direction to drive valve 32 open and cause a further rebalancing by wiper 42.

If now, while on the heating cycle, the relative humidity should ris above the desired value and element 66 elongate and permit closure of the contacts of switch 65, the refrigerating apparatus isthen put in operation by the circuit: secondary winding I33, wire 2I1, wire 22I, switch 65, Wire 222, winding 2I2 of relay 2, wire 223, wire 224 and secondary winding I33. Energizing winding 2I2 closes switches 2I3 and I68 and, because switch 2 I3 is connected in parallel with switch 23-, it causes operation of the refrigerating system, as previously described. Further, closing switch I 68 shunts resistor I66, thereby reducing the reslstance between resistor 9I and input terminal 8i, this having the same effect as reducing the resistance of resistor BI, and acting in a similar fashion to a reduction in space temperature. This calls for additional heating because wiper 3i is thus made more negative relative to ground 5I than it was previously, and due to the higher control point thus established for room temperature responsive resistor 9 l additional heat is provided by coil 5 to oiiset the cooling effect of evaporator I5. As before described, operation of the refrigerating apparatus tends to condense moisture out of the air passing through the coil and the subsequent reheating of the air then reduces the relative humidity.

Assuming the relative humidity now decreases below the set point of humidistat 62, so that the contacts of switch 55 are opened, relay 2H is deenergized and the refrigerating apparatus is stopped. In addition, switch I58 is opened, thereby reestablishing the normal control point for resistor 91.

At the same time that wiper 33 is connected to input terminal 35 of amplifier 35, wiper N5 of potentiometer iiE is connected to the input terminal 55 of amplifier 53 by a circuit previously traced. However, so long as wiper Si is able to rebalance the network, wiper H3 remains negative relative to ground and, as before mentioned, a negative signal on input terminal 55 of amplifier 53 is unable to cause operation of relay 54. However, if the internal heating load of the structure being treated should vanish and the inside temperature continue to rise, although the outside temperature is still low enough to call for heat, the rise in room temperature causes an increase in resistance of resistor 3i and tends to make wiper 3? positive, and a positive signal impressed on input terminal 48 of amplifier 45 causes relay 43 to energize motor 33 in a direction to close valve 32 by a circuit similar to that of the previous example. closing valve 32 and advancing wiper 37 to the extreme right of resistor 39, no further rebalancing of the network can take place, and upon a suificient increase in room temperature to overcome the potential existing between wiper 37 and wiper W8, wiper H3 then becomes positive relative to ground and a positive signal is impressed on input terminal 55 of amplifier 53, thus causing the energizing of relay 54 of said amplifier. Upon relay 54 on amplifier 53 being energized, the refrigerating apparatus is placed in operation by the circult: secondaiy winding I33, wire 2H, wire 228, wire 22?, relay 54, wire 228, winding 28 of relay 24, Wire 2223 and secondary winding I33, energizing winding 28 of relay closing switch 23 and operating the refrigerating apparatus, as previously described. Obviously, as the operation of th refrigerating apparatus diminishes room temperature and thereby decreases the resistance of resistor 9i, wiper H8 then becomes less positive relative to ground hence, upon the positive signal being wiped out, due to the decrease in resistance of resistor 9i, relay 54 is deenergized and relay 24 then drops out, stopping the refrigerating apparatus.

If the outside temperature should now rise above a predetermined value, such as 70 degrees, and switch 254 of thermostat 215 is closed, winding 229 of relay I8I is energized by the circuit: secondary i33, wire 2H, wire 235, winding 229, wire 23I, switch 2I4 and wire 232 to ground wire 50. This causes switch blades I82 and I85 to engage in" contacts I91 and I99 of said relay and shift control of amplifiers 45 and 53 from one However, upon motor 33 completely 12 branch of the network to the other branch of said network. Thus, wiper 42 of rebalanced potentiometer 35 is connected through wire I98, in contact I99, blade I and wire 206 to input terminal 6-53 of amplifier '55, and wiper I55 of potentiometer IE2 is connected through wire I96 and in contact 9! to blade I82 which is connected to input terminal 55 of amplifier 53, as previously described. This branch of the network is generally similar to that previously described excepting that compensator ESB is in the opposite side of the bridge from compensator I'I'S, hence the resistance of SI must now be increased more than that of resistance I88 to cause a positive signal to be impressed on input terminal 48. However, assuming that the space temperature does rise without a similar rise in outside temperature, then wiper 42 is positive relative to ground 5|. As before noted, a positive signal on wiperv 42, and thus on input terminal 48 of amplifier 45 causes an energization of motor 33 in a direction to close valve 32 and to move wiper 42 to its right extreme. However, assuming that wiper 42 is already at its right extreme, a sufiicent unbalance of the network, due to a sufficiently high temperature at 9I, causes wiper I to become positive relative to ground 5| and thereby imposes a positive signal on input terminal 55, by a circuit previously traced. A positive signal on the input of amplifier 53 causes energization of relay 5d and thus causes operation of the refrigerating apparatus, in a manner previously described. The refrigerating apparatus then operates until the room temperature is reduced or until the outside temperature increases the resistance of resistor I88 to thereby tend to make wiper I55 negative relative to ground and drop out relay 54.

While operating on the cooling cycle, an increase in relative humidity causes a closing of switch 55 which thereby causes an energization of winding 2l2 of relay 2H and a consequent closing of switch 2I3, but this switch may have no eifect in starting the refrigerating apparatus if it is already in operation. However, on the normal cooling cycle, the refrigerating apparatus would be cycled on and off to maintain the space temperature at the desired value. However, with the switch 2I3 kept closed by humidistat 62, the apparatus continues in operation even though the space temperature tends to be satisfied. However, as the space temperature is lowered, thereby eliminating the positive signal from wiper I95 and dropping out relay 54 of amplifier 53, a further drop in space temperature will cause wiper 42 to become negative and thereby cause energization of motor 33 in a direction to open valve 32 and cause heating by coil H5. The opening of valve 32 is accompanied by movement of wiper 42 to the left across resistor 39 to rebalance the network, as previously described. The continued operation of the refrigerating apparatus and the reheating of the air to maintain space temperature causes a decrease in relative humidity and eventually satisfies humidistat 62, causing an opening of switch 55 and a stopping of the compressor, providing that the space temperature is not calling for cooling.

Summary In the above disclosure, it is shown how an air conditioning apparatus can be controlled on either a heating or cooling sequence with outside compensation in either case and with the compensation in the desired direction and of the amount desired. In addition, the system can be operated on a reheat cycle regardless of whether the normal cycle is heating or cooling, if such a reheat cycle is necessary to correct relative humidity conditions. Also, the capacity effects involved in the complex network described due to unsymmetrical leads and the like are readily balanced by a capacity balance potentiometer and capacitor connected across the input terminals of the network.

The examples given of the present invention are only illustrative and it is obvious that many substitutions and equivalents will appear to one skilled in the art hence the scope of this invention should be determined only by the appended claims.

I claim:

1. In control apparatus for an air conditioning system, an electrical network circuit having a plurality of parallel branches, input connections for said network circuit, one of said parallel branches including a first temperature responsive impedance having a relatively high impedance value and a first output connection, another of said branches including a compensating second temperature responsive impedance and a plurality of other output connections, said con nections being between said second impedance and one of said input connections, said second impedance having an impedance value less than that said first impedance, an additional branch of said network circuit including a compensating third temperature responsive impedance and an additional output connection, said third impedance also having an impedance value less than that of said first impedance and being connected in the circuit to compensate in a different manner than does said second impedance, a heating control device, switching means operated by said heating control device, a cooling control device, amplifier means for controlling said devices, electric circuit means including a relay for connecting said other or additional output connections of one or the other of said parallel branches in controlling relation to said amplifier means, said first output connection also being connected to said amplifier means and being common to said net work circuit, humidity responsive means, and means connecting said humidity responsive means and said switching means in controlling relation to said relay means.

2. In control apparatus for an air conditioning system, in combination, an alternating current electrical network circuit, input connections for said circuit, said circuit having a plurality of parallel branches, one of said branches including a first condition responsive impedance, said one branch including an output connection common to the network as a whole, another of said branches including another output connection and a second condition responsive impedance, said second impedance being arranged to act as a compensator for the first impedance, an additional branch of said network circuit including an additional output connection and a third condition responsive impedance for compensating said first impedance, said third impedance being arranged on a side of said additional output connection opposite to the arrangement of the other output connection and said second impedance, one of said impedances being appreciably more distant from the input connections than another of said impedances, a further parallel branch including a high resistance resistor having an adjustable intermediate connection, a capacitor,

means connecting said capacitor in series with said intermediate connection and said common output connection, and amplifier means controlled by the common and said other and said additional output connections.

3. In control apparatus for an air conditioning system having both heating and cooling equipment, in combination, an electrical network circuit, said circuit having a plurality of parallel branches, input connections for said circuit, one of said branches including a first condition responsive impedance, said one branch including an output connection common to the network circuit, another of said branches including another output connection and a-second condition responsive impedance, said second impedance being arranged to act as a compensator to the first impedance, an additional branch of said network circuit includin an additional output connection and a third condition responsive im pedance for compensating said first impedance, said third impedance being arranged on a side of said additional output connection opposite to the arrangement of said second impedance and said other output connection to thereby compensate the first condition responsive impedance in a direction opposite that of the second condition responsive impedance, an amplifier means capable of controlling heating equipment, another amplifier means capable of controlling cooling equipment, means connecting said common output connection to both of said amplifier means, and means connecting said second and third output connections to said heating and cooling amplifier means respectively.

4. In control apparatus for an air conditioning system, in combination, an electrical network circuit, input mean for said circuit, said circuit having, a plurality of parallel branches, one

of said branches including a first condition re-v sponsive impedance, said one branch including an output connection common to said circuit, another of said branches including another output connection and a second condition responsive impedance, said second impedance being arranged to act as a compensator for the first impedance and having a lower impedance value than said first impedance, an additional branch of said network circuit including an additional output connection and a third condition respon-' sive impedance for compensating said first impedance, said third impedance also having a lower impedance value than said first impedance value and being arranged on a side of said additional output connection opposite to the arrangement of the other output connection and said second impedance to thereby compensate said first impedance in a direction reverse to that of the second impedance, separate amplifier means individually controlled by the common and said other and said additional output connections, a heat control device controlled by one of said amplifier means, and a cooling control device controlled by another of said amplifier means.

5. In control apparatus for means for changing a condition in opposite directions, in combination, an electrical network circuit having more than two output connections, input means for said circuit, said circuit having a plurality of parallel branches, one of said branches including a first condition responsive impedance, said one branch including one of said output connections used as a common output connection, another of said branches including another of said output connections and a second condition responsive impedance, said second impedance being arranged to act as a compensator for the first impedance, an additional branch of said network circuit including an additional one of said output connections and a third condition responsive impedance for compensating said first impedance, said third impedance being arranged to compensate said first impedance differently than does said second impedance, an amplifier means capable of controlling condition changing means of one sort, additional amplifier means capable of controlling condition changing means of a different sort, means connecting said common output connection to both of said amplifier means, and means connecting said second and third output connections to said respective amplifier.

6. In control apparatus for an air conditioning system, an electrical network circuit having a plurality of parallel branches and at least three output connections, input connection for said network circuit, one oi said parallel branches including a first condition responsive impedance and one of said output connections used as a common output connection, another or said branches including a compensating second temperature responsive impedance and a plurality of said output connections, said connections being between said second impedance and one of said input connections, an additional branch of said network circuit including a compensating third temperature responsive impedance and an additional one of said output connections, said third impedance being arranged in said branch to compensate said first impedance in a different manner than does said second impedance, a heating control device, a cooling control device, separate amplifier means for controlling each of said de vices, electric circuit means connecting said common output connection to both of said amplifier means, means connecting one of the output connections of said second branch to one or said amplifier means and the other output connection of said second branch to the other amplifier means, and means capable of connecting the output connection of said third branch to one of said amplifier means.

'7. In control apparatus for an air conditioning system, an electrical network circuit having a plurality of parallel branches and more than two output connections, input connections for said network circuit, one or" said parallel branches including a first temperature responsive impedance and one of said output connections used as a common output connection, another of said branches including a compensating second temperature responsive impedance and a plurality of said output connections, said connections being between said second impedance and one of said input connections, an additional branch of said network including a compensating third temperature responsive impedance and an additional one of said output connections, said third impedance being connected in the network in a manner to modify the influence of said fi st impedance in a different manner than does said second impedance, a heating control device, switch means operable by said heating control device, a cooling controlling device, separate amplifier means for controlling each of said devices, circuit means for connecting said common output connection to both of said amplifier means, means connecting the output connections of said second and third branche to control both of said amplifier means, and relay means controlled by said switch means for shifting control of one iii of said amplifier means from one output connection to another output connection.

8. In control apparatus for an air conditioning system, an electrical network circuit having a plurality of parallel branches and more than two output connections, input connections for said network circuit, one of said parallel branches including a first temperature responsive impedance and one of said output connections used as a common output connection, another of said branches including a compensatil'lg second temperature responsive impedance and a plurality of said output connections, said connections being between said second impedance and one of said input connections, an additional branch of said network circuit including a compensating third temperature responsive impedance and an additional one of said output connection, said third impedance being connected in its branch in a manner to modify the influence of said first impedance in a different manner than does said second impedance, a heating control device, a cooling controlling device, a plurality of amplifier means for individually controlling said devices, electric circuit means connecting said output connections in controlling relation to said amplifier means, and humidity responsive means for controlling an electric connection in shunt relation to one of said amplifier means for directly controlling a cooling controlling device.

9. In control apparatus for an air conditioning system, an electrical network circuit having a plurality of branches and more than two output connections, input connections for said network circuits, one of said branches includin a first temperature responsive impedance and one of said output connections used as a common output connection, another of said branches including a compensating second temperature responsive impedance and a plurality of said output connections, said connections being between said second impedance and one of said input connections, an additional branch of said network circuit including a compensating third temperature responsive impedance and an additional one of said output connections, said third impedance being constructed and arranged to compensate said first impedance in a difierent manner than does said second impedance, a heating control device, a cooling controlling device, amplifier means for controlling said devices, elec tric circuit means connecting said output connections in controlling relation to said amplifier means, and temperature responsive means exposed to outside air for controlling said electric circuit means in a manner to shift control of at least part of said amplifier means from the output connections of one of said branches to the other.

10. In control apparatus, an electrical network circuit having a plurality of parallel branches and more than two output connections, input connections for said network circuit, one of said branches including a first temperature responsive impedance and one of said output connections used as a common output connection, another of said branches including a compensating second temperature responsive impedance and a plurality of said output connections arranged in electrically spaced relation to each other, an additional branch of said network circuit including a compensating third temperature responsive impedance and a 13 rality of said output connections also arrang d in electrically spacedrelation to each other, said third impedance being arrangedito compensate said first impedance in a reverse manner than said second impedance a heating control device, a cooling control.device separate amplifier means connected in controlling relation to each of said devices, electrical circuit-means including a relay for connecting the output connections of either the otheror theadditional branchin controllin relation to theseparate amplifier means to thereby alter the sequence of controlto be effected by the presentapparatus, and meansresponsive to the same temperature as one of said second or third. impedances for controlling said relay.

11. In control apparatus, an alternating cur rent electrical network circuit having a plurality of parallel branches and morethan two output connections, input connections for said network circuit, one of said branches including a first condition responsive impedance and one of said output connections used as a common output connection, another of said branches including a compensating second condition responsive in.- o ance and a plurality of said output connecns, an additional branch ofsaid network circuit including a compensating third condition responsive impedance and a plurality of said output connections, said third impedance being ar ranged to compensate said first impedance in a different manner thansaid second impedance, a further branch including the resistor'of a potentiometer, a capacitor, means connecting the wiper of said potentiometer and said capacitor in series with said common output connection, a heating control device, acooling control device, separate amplifier means connected in controlling relation to each or" said devices, electric circuit means including a relay for connecting the output connection of either the other or the additional branch in controlling relation to the separate amplifiers to thereby control said amplifier in a sequence depending on which network branch is used, and means responsive to the same condition as one of said second or third impedance-s for controlling said relay.

12. In control apparatus, an electrical network circuit having a plurality of parallel branches and having a plurality of output connections, input connections for said network circuit, one of said branches including a first condition responsive impedance and one of said output connections used as a common output connection, another or" said branches including a compensating second condition responsive impedance and a plurality of said output connections, an additional branch of said network circuit including a compensating third condition responsive impedance and a further plurality of said output connections, said third impedance being arranged to compensate said first impedance in a different manner than said second impedance, a heating control device, a cooling control device, ampliiier means for controlling said devices, electrical circuit means including a relay for connecting the output connections of either the other or the additional branch in controlling relation to said amplifier means to thereby alter the sequence of control to be effected, means responsive to the same condition as one of said second or third impedances for controlling said relay, and huinidity responsive means for independently controlling said cooling control device.

13. In control apparatus for an air conditioning system having heating means and cooling 18 me ans,,me ans including anetwork circuithaving a plurality of parallel branches for controlling said heatingmeans and said cooling means, one of said parallel branches ,ha-vingan output connection for'said coolingmeans and another of said branches having an output connection for said heating means, relay means Q'Dfirableto connect said means including anetwork circuit to said heatingmeans in a manner to cause normal operation of the heating means when there is a heating. load and operable to connect said means includin thB1IIEfiWOIK. circuit to said cooling means in a manner to cause normal operationbf the cooling system when there is a cooling, load, additional relay means, humidity responsive means for operating said additional relaymeanajandmeans connecting said additional relaymjeans to said control apparatus in a mannerto' cause simultaneous operation of said heating means and said cooling means when the relative humidity affecting said humidity'res'ponsive means reachesa predetermined value.

14. In control apparatus foran air conditioning system having, heating, meansan'd cooling means including an electrical impedance means responsive to the temperature of the space being treated, ,a deviceresponsive to the relative humidity in said space, switchgmeans operable by said, humidity responsive device, means includinga network. circuit for controlling saidheatingmeansand said cooling means, said circuit including said impedance means and at least a pair of electrical potential spaced output connections andanother output connection used with either or both of the first named output connections, said means including said network circuit and its output connections being connected to normally control said heating means and said cooling means in sequence, means connecting said switch means to said means including said network circuit and its output connections in such manner that said cooling means and said hea ing means are operated simultaneously when said humidity responsive means responds to a pred termined value of humidity.

15. In air conditioning control apparatus, a device for controlling heating and a device for controlling cooling, impedance means responsive to the temperature of the space being conditioned, a plurality of impedance means responsive to the temperature of the air supplied to said air conditioning apparatus, relay means for controlling said heating control device and said cooling control device, and a network circuit having a plurality of parallel branches, one of said branches being connected to an output connection designated a common output connection, separate output connections for each of the other of said branches, said one branch including said space temperature responsive means, one of said other parallel branches including one of said supply air temperature responsive means and an output connection connected to said relay means for controlling said heating control device, said supply air temperature responsive device being arranged in said network circuit in a manner to compensate said circuit in a manner tending to require an increased spaced temperature as the air supply temperature decreases, and another one of said other said parallel branches including another of said supply air temperature responsive means and an output connection connected to said relay means for controlling said cooling control device, the last named supply temperature responsive means being arranged in said network circuit in a manner to compensate said network in a manner tending to require an increased space temperature as said supply air temperature increases, said common output connection being used with either of the separate output connections.

16. In control apparatus, a balanceable electrical network circuit having a, common output connection and a plurality of other output connections, a corresponding plurality of control devices each connected to one of said other output connections and to said common connection, an alternating current source for said network circuit, and a capacity balance means for said network comprising a potentiometer and a capacitor, said potentiometer including a resistor connected to said current source in shunt relation with said network and the wiper of said potentiometer and said capacitor connected in series with said common connection.

17. In control apparatus, a balanceable electrical network circuit having a common output connection and a plurality of other output connections, a pair of input terminals for said network arranged to be connected to a suitable source of alternating current electricity, and a capacity balance means comprising a potentiometer and a capacitor, the resistor of said potentiometer being connected across said input terminals and the wiper of said potentiometer being connected through said capacitor to said common connection.

18. In control apparatus for air conditioning apparatus including a heating means and a cooling means, relay means for controlling said heating means, another relay means for controlling the cooling means, and means including a network circuit for controlling both of said relay means, said network circuit including a pair of output connections arranged in the circuit to be at different electrical potentials, said network circuit also having another output connection, one of said pair of output connections and said other output connection being connected in controlling relation to the relay means for said heating means and the other of said pair of output connections and said other output connection being connected in controlling relation to the relay means for said cooling means.

JAMES W. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,144,105 Coleman Jan. 17, 1939 2,286,029 Haines Dec. 16, 1941 2,282,442 Whitlock May 12, 1942 2,298,847 Smith Oct. 13, 1942 2,346,592 Lehane et al. Apr. 11, 1944 2,362,977 Crosthwait et a1. Nov. 21, 1944 2,372,839 McGrath Apr. 3, 1945 2,375,988 Gille et al May 15, 1945 2,457,165 McNamee Dec. 28, 1948 2,462,599 Blumlein et al. Feb. 22, 1949 2,486,908 Andersson Nov. 1, 1949 FOREIGN PATENTS Number Country Date 527,349 Great Britain Oct. 7, 1940 

